Yes, there is supply and demand. However, that doesnt mean a government cant restrict supply.

It precisely and explicitly demands that the government restrict supply of foreign labor, as that increases the fair market value of American wage earners. It increases the opportunities for young Americans to trade their labor for a start in life, to support their families, and to make our nation stronger. Importing foreign labor makes it more difficult to justify hiring Americans, and undermines the nation's long term success for short term gains. It is effectively an Anti-investment.